পাতা:পদার্থবিদ্যাসার.djvu/৩৭

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26 Pup. What are the spots in the moon supposed to be * - ; , , , , Tut. They are supposed to be mountains. The dark parts were formerly imagined to be seas ; but from later observation, it is proved, that they are hollow places or caverns, which do not reflect the light of the sun. - Pup. Do yoti also snppose the planets of other systems, to which the stars are suns, are inhabited Tut. Without doubt. Such an idea is truly philosophical, grounded upon reason and analogy. As othere is such an amazing variety and gradation in the animal species, so it is not to be supposed that men are the only intelligent beings in the universe. Pup. What idea am I to form of the comets; are they bodies of fire? * . . Tut. No. They receive their light from the sun, which is apparent from their shining trains. Pup. Are not those trains, or tails, fire? Tut:” They are conjectured to be only their atmospheres, enlightened by the sun. . . . . . . " . Pup. Are not the comets supposed to pass for beyond the limits of the most distant planet? Tut. Yes, which serves to give us a very, enlarged idea of the extent of the firmament. The period of that . cemet's rev olution ..which appeared in 1758, Y೫, computed at about seventy-five years; and ta which was seen in 1880, has been shown to have a period of more than'five huñdred and seventy-five years.” The orbits of some other coinets' have been fixed with sufficient àeeuracy to atertain when they may be expected to appear again. . . . * * **** *::::